I. Field of the Invention:
This invention relates generally to a cooking appliance and more specifically to a food rotator for use in an oven which functions to ensure that the item being prepared will be more uniformly exposed to the infrared or microwave energy during the cooking operation.
II. Discussion of the Prior Art:
Turntables for use in an oven environment to provide more uniform cooking is an old concept. The Shaw U.S. Pat. No. 557,344 describes a turntable device having a spring motor for rotating the table and it dates back to the late 1800's. At that time, most ovens were wood or coal fired, and, as such, the heat was not evenly distributed within the oven chamber. By rotating the food while cooking, it would be more uniformly exposed to the infrared energy.
With the advent of natural gas and electric ranges, it became possible to design the burner arrangement such that the heat was uniformly distributed within the oven chamber. Hence, the need for a food rotator device was obviated. However, in the late 1940's or early 1950's when microwave ovens came into vogue, it was discovered that the microwaves are not uniformly distributed within the oven enclosure and, as a result, so-called "hot spots" developed whereby the cooking was not uniform throughout the article being heated. Thus, the turntable approach again came into popularity.
The U.S. Pat. No. 4,036,151 to Shin, describes a microwave oven having a built-in turntable structure. During the 1970's built in turntables were primarily found in microwave ovens of Japanese manufacture. United States manufacturers, however, attempted to solve the "hot spot" problem by addressing the manner in which the microwaves could be distributed within the oven cavity. So-called "mode stirring" devices were built into the ovens. This approach has not been altogether satisfactory and many thousands of microwave ovens have been sold and are in use which do not adequately distribute the microwave energy throughout the oven cavity and which do not include a built-in turntable.
Various portable food rotator devices have been devised for use in microwave ovens. The Beh et al. U.S. Pat. No. 4,254,319 describes a turntable device driven by a spring-type motor wherein all of the parts comprising the motor and escapement are fabricated from a plastic that tends not to heat up when exposed to microwave energy. This device did not become a commercial reality, it is believed, because of the inability of a plastic spring to store sufficient energy for rotating the turntable over a prolonged period.
The Cunningham U.S. Pat. No. 4,239,009 is another example of a prior art design that was commercially impractical because it employs a standard spring motor and escapement construction using metallic parts but without providing shielding of any type. As a result, when exposed to microwave energy, the metallic parts produce considerable arcing, sparking and overheating.
In accordance with our earlier invention which is described in U.S. Pat. No. 4,258,630, a solution was provided whereby metal spring motors could be placed within the microwave oven cavity without exhibiting the drawbacks attendant in the device of the Cunningham Patent. Specifically, the spring motor is disposed beneath the rotatable turntable and is contained within a smooth metallic container having no sharp edges to serve as high potential discharge points. Having solved that problem, Applicant's Assignee, Northland Aluminum Product Inc., has been highly successful in selling its MICRO-GO-ROUND.RTM. turntable for use in microwave ovens where they do not have a built-in food rotator.
Microwave ovens for home use have a relatively small oven compartment and, as such, it is desirable that the turntable present a low profile so as not to take up room which could otherwise be used to contain the food items to be cooked. The Pomeroy et al. U.S. Pat. No. 4,330,696 attempts to address this problem by relocating the drive motor assembly so that it does not fit beneath the rotatable table itself. Instead, the motor assembly is housed separately from the turntable structure and is positioned alongside the turntable rather than beneath it. The drive assembly is coupled through a suitable spur gear to cooperate with gear teeth formed on the rim of the turntable element itself. The underlying theory in the design of the device described in the Pomeroy Patent is that the motor assembly is positioned in a corner of the microwave oven and, accordingly, is supposedly less obtrusive both in terms of occupying space which would otherwise be available for food placement and in terms of being located in a zone where microwave energy is of lowest density. In practice, however, the positioning of the drive unit alongside the turntable itself still interferes with the free rotation of certain food items when placed on the turntable beyond that which is dictated by the corners of the oven itself.
It can be seen, then, that it is desirable to provide a turntable having a low height profile but with the drive assembly for the turntable being disposed beneath the rotatable table portion of the device. In this way, large casseroles, roasts and fowl will still fit within the oven space and will rotate freely without interference from any upwardly projecting drive elements of the turntable.